The present invention relates generally to heat exchangers. More particularly, the present invention relates to heat exchangers through which a refrigerant flows in heat exchange contact with ambient air flowing over an external surface thereof. With still more particularly, the present invention relates to a heat exchanger for an outdoor unit of an air conditioner or heat pump which employs tubing having multiple discrete flow paths for refrigerant therethrough and onto which so-called spine fin heat transfer surface is wrapped or otherwise bound.
The use of heat exchangers having a spine fin heat transfer surface in certain air conditioning applications is known as is the use of so-called microchannel tubing in certain other and different heat exchanger applications. Exemplary of the use of spine fin heat transfer surfaces in the outdoor heat exchanger coils of residential air conditioners is U.S. Pat. No. 4,535,838, assigned to the assignee of the present invention and incorporated herein by reference. It will be noted that in prior spine fin applications, tubing which is circular in cross-section and which defines a single internal refrigerant flow passage has been the norm.
Microchannel tubing is known to be used in automotive radiators. The design of such radiators calls for the brazing of fins, in a controlled fashion utilizing relatively expensive and energy consuming brazing furnaces, to the microchannel tubing or for the mechanical deformation of the tubing or its fins so as to rigidly ensconce the tubing in the fin surface with which it is used. The latter is illustrated by U.S. Pat. No. 3,603,384.
Heat exchangers have also been made using microchannel tubing in which heat transfer fins are formed by a process of gouging or otherwise forming the exterior surface of tubing itself so as to create fin-like projections. Illustrative in that regard is U.S. Pat. No. 3,886,639.
A need has been identified to minimize the operating refrigerant charges used in air conditioning units, heat pumps, and other such apparatus of the type used to cool and/or heat homes and small commercial establishments and to reduce or at least maintain the costs associated with the manufacture of such devices. This need arises from the increasing expense of raw materials used in the manufacture of heat exchangers for use in such applications, from increased prices for existing refrigerants, from the introduction of newer, higher pressure refrigerants and from a demand for more compact and less obtrusive outdoor units where the space in which to dispose such units may be at a premium. Existing outdoor heat exchanger coils for such applications are not sufficiently strong, economical of manufacture or efficient from a heat exchange standpoint to meet all of such demands.